• Mayuri Vaish

Neural effects of marijuana: Current research summarized

Updated: Dec 11, 2018

THC has a variety of effects on the nervous system that impacts learning, either directly or indirectly, and there is an incredibly large amount of research regarding the effects of marijuana on the brain.

Essentially, consuming Marijuana is a slippery slope due to its addictive nature (and thus not recommended), resulting in a loss of ability to concentrate. This is due to its primary active component, Tetrahydrocannabinol (THC). On consuming marijuana, THC travels from lungs to the bloodstream, through which it may permeate the neurons via the blood brain barrier.

At the cellular level, within the neurons, THC resembles Anandamide, a naturally-occurring endocannabinoid in the brain. Endocannabinoids are neurotransmitter chemicals that bind to cannabinoid receptors of post-synaptic neurons in the brain, producing feelings of pleasure[1][2][3] .

THC binds to receptors in the postsynaptic neuron, resulting in the blocking of Calcium channels that are normally used to excite the pre-synaptic neuron and initiate neurotransmitter release. Thus, less excitatory neurotransmitter is released, resulting in an inhibitory, sedative effect[4], which is partly why it is used for medical purposes, as a muscle relaxant, or for anxiety[5] .

Due to this loss of excitation, THC also impairs movement, thinking, memory (which is largely produced by an excitatory neurotransmitter, glutamate), and other bodily functions, and thus definitely does impact one’s ability to learn immediately after consumption.

Moving on from its cellular effects, the actual regions of the brain at which these effects are produced are also largely responsible for the specific feelings of ‘high’ received when consuming marijuana. These locations are shown below[6]:

General parts & functions of the brain

Notable areas include the Ventral Striatum and Ventral Tegmental Area (VTA)[7][8], where it was shown to increase dopamine transmission by reducing the release of GABA (an inhibitory neurotransmitter), thus producing greater feelings of pleasure and reward - leading to highly addictive behaviors that could impact one’s ability to stay focused.

Another area impaired by THC is the hippocampus[9][10][11] , which plays an important role in preserving memory. Hippocampal neurons have been found to contain reduced synapses, to be of smaller sizes, and decreased dendritic length. Hippocampal protein expression was more notable in adolescents[12], and THC-exposed monkeys showed impaired spatial working[13]. This loss in memory and spatial recognition obstructs one’s ability to learn and recall information, thus reducing his or her learning outcomes.

However, there is some evidence that counters the above claims, resulting in a need for further research. Studies have found no significant structural differences of marijuana users and non-users[14], and a twin study suggested that other factors apart from marijuana may result in decreased adolescent IQ[15].

Marijuana can also definitely reduce the learning capacity of babies. THC use during pregnancy has shown to increase risks of brain damage and underdeveloped physiology in babies[16]. Marijuana can be exposed to developing babies by placenta, where it can lead to increased hyperactivity, impulsivity, and lack of attention[17]. Moreover, marijuana-exposed developing children performed poorly on cognitive tests[18].

Lastly, THC could also hinder overall health by resulting in nausea, coughing and gastro-intestinal problems, known as the Cannabinoid Hyperemesis Syndrome.[19]. These problems could significantly impact one’s ability to learn promptly.

THC, has also shown to have lead to phenotypes resembling autism and schizophrenia[20][21][22], and to have accelerated neural death[23].

These are only some of the possible mechanisms and effects of THC, and research is still ongoing. However, overall, there is strong overall evidence to show impaired learning after marijuana consumption - particularly in one’s adolescent years - and the dose dependency of these effects are yet to be fully understood.


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